1. Field of the Invention
The present invention relates to a fringe field switching liquid crystal display (FFS-LCD), and especially to a transflective mode FFS-LCD providing low power consumption.
2. Description of Prior Art
The in-plane switching liquid crystal display (IPS-LCD) has been developed in order to improve on the narrow viewing angle of the standard twisted nematic liquid crystal display (TN-LCD). The IPS-LCD has a counter electrode and a plurality of pixel electrodes all disposed on a same substrate of two opposite substrates, for driving liquid crystal molecules that are disposed between the substrates. The resulting electric field is substantially planar and parallel to a surface of said same substrate. This structure provides an improved viewing angle.
However, the counter electrode and pixel electrodes are formed of opaque metals, giving the IPS-LCD a low aperture ratio and low transmittance. Thus the so-called fringe field switching liquid crystal display (FFS-LCD) has been developed in order to improve on the aperture ratio and transmittance of IPS-LCDs. The FFS-LCD is characterized by the liquid crystal molecules being driven by a fringe electric field.
Referring to FIG. 7, this is a cross-sectional representation of an FFS-LCD as disclosed in U.S. Pat. No. 6,642,985 issued on Nov. 4, 2003. The FFS-LCD 10 is a transmissive mode LCD, which utilizes a backlight as a light-illuminating section. The FFS-LCD 10 comprises an upper substrate 11 and a lower substrate 1 disposed opposite to each other and spaced apart a predetermined distance. A liquid crystal layer 20 having a plurality of liquid crystal molecules 20a is disposed between the upper and lower substrates 11, 1. A counter electrode 2 and pixel electrodes 4 are disposed on the lower substrate 1, with an insulating layer 3 interposed between the counter and pixel electrodes 2, 4. A lower alignment film 5 is disposed on an inner surface of the lower substrate 1. A color filter 14 is disposed on an undersurface of the upper substrate 11. The color filter 14 comprises a black matrix 12, and a color resin layer 13 having Red, Green and Blue segments. An indium tin oxide (ITO) layer 30 and an upper alignment film 15 are disposed at an underside of the color filter 14, in that order from top to bottom.
The counter electrode 2 is essentially planar, and each pixel electrode 4 is comb-shaped. The counter electrode 2 and the pixel electrode 4 are transparent conductors, which are made of a material such as ITO. Therefore, the aperture ratio of the FFS-LCD 10 is improved compared to that of an IPS-LCD. The pixel electrode 4 partially overlaps the counter electrode 2, and a distance between the counter electrode 2 and the pixel electrode 4 is less than that between the lower substrate 1 and the upper substrate 11. When the FFS-LCD 10 is driven, a fringe electric field is formed at upper portions of the counter electrode 2 and the pixel electrode 4. The liquid crystal molecules 20a disposed over the counter and pixel electrodes 2, 4 are all driven, thus giving the FFS-LCD 10 improved transmittance compared to that of an IPS-LCD.
However, the FFS-LCD 10 is a transmissive mode LCD, in which a backlight is utilized as a light-illuminating section. The backlight typically consumes 50% or more of the total power consumed by the FFS-LCD 10.
It is desired to provide an FFS-LCD that can solve the above-mentioned high power consumption problem.